(1) Field of the Invention
This invention relates to a composition of matter and a process for using same, and more particulary to an antifouling composition of treating nets, and in particular aquaculture, fish cages and weir fishing nets which are stationary, undecorative fishing nets.
(2) Description of the Prior Art
It has been found that many types of nettings, exposed to sea and fresh waters, experience heavy levels of clogging due to algae and invertebrates. Such clogging limits the flow of water and deposited organisms on the net can cause weight increases as high as 1000 percent. Such a weight increase results in the sinking of the supported netting and fish escape as well as making it practically impossible to raise the netting for cleaning. In some instances, the cutting away of netting is necessitated, resulting in the loss of netting. In addition to netting losses, fish may also be lost or harmed. Salt and freshwater aquaculture systems have traditionally been plaqued by heavy fouling on nets, cages, intake pipes and aeration systems.
Nets, particularly, have suffered from heavy encrustation, making them inordinately heavy, and eventually incapable of permitting water flow-through. Natural food penetration, acceptable oxygen levels, removal of fish wastes and detritus removal are severly restricted, leading to loss of or poor crop yield. Labor for frequent cleaning adds high costs, and full cage utilization is not possible because of cage rotation during cleaning. Antifouling compounds have been used for centuries with only partial success. Traditional antifouling coating treatments have relied on copper oxide and mercury compounds and other heavy metal compounds which are effective antifoulants, but are highly toxic and can be damaging to systems in which live organisms are expected to survive.
In U.S. Pat. No. 4,393,102 to Guglielmo, Sr. there is disclosed a net finishing composition in a suitable solvent system which, when coated on a net substrate, particularly a nylon net substrate of a mesh size of from 1/4 to 5 inches, substantially improves the integrity of the net substrate. The net fishing composition is comprised of a low molecular weight, high acetate content, vinyl chloride copolymer, a monomeric plasticizer, and a polymer plasticizer. The molecular weight of the copolymer is from 20,000 to 65,000 and of an acetate content of from 10 to 20 percent by weight. The plasticizers are present in an amount of from 40 to 60 parts, preferably 50 parts per 100 parts of the copolymer with the ratio on monomeric plasticizer to polymeric plasticizer ranging from about 1:1 to 3:1, preferably 2:1. It is also disclosed that antifouling properties could be improved by adding certain organo-tin esters dissolved or dispersed in the solvent system.
In U.S. Pat. No. 4,661,400 to Guglielmo, Sr. there is disclosed a net antifouling composition for use on nettings and comprised of from 2 to 10 percent, preferably 3 to 6 percent by weight of a tri-n-butyl tin ester selected from the group consisting of tri-n-butyl tin linoleate, bis(tri-n-butyl) tin succinate, tri-n-butyl tin benzoate, bis(tri-n-butyl) tin salicylate and mixtures thereof in an organic solvent system or a water base system, preferably a water base system, for controlling algae and invertebrate growth.
While the tri-n-butyl tin esters have proven to be exceedingly effective agents in antifouling compositions, the tri-n-butyl tins have demonstrated adverse ecological problems, particularly with respect to shellfish, notwithstanding the fact that the organo-tin esters are biodegradable to elemental tin, an element which is naturally occuring in the environment. Tin, along with copper, zinc and iron, is distributed in nature and in foods, such as fish flour rice, milk, seawater, etc. While copper oxide based paints, as well as tars, have been shown to result in high kill levels of fish fry as well as demonstrated carcinogenicity, the organo-tin compounds have not demonstrated like adverse effects on fish; however, they have adversely effected non-target shellfish. Accordingly, the E.P.A., and like governmental bodies of foreign countries, have placed the organo-tin compounds on the prohibitive list of active antifouling ingredients.